The present invention relates generally to apparatus and methods for treating spinal disorders, and more particularly to anchor screw assemblies, spinal fixation systems including such anchor screw assembles, and methods for stabilizing, adjusting, or otherwise fixing adjacent vertebrae using such spinal fixation systems.
Various systems and methods have been suggested for treating spinal disorders, such as degenerative discs, stenosis, trauma, scoliosis, kyphosis, or spondylolisthesis. For example, U.S. Pat. No. 5,545,166, naming the same inventor as the present application, discloses a spinal fixation system that includes a plurality of anchor screws, clamp assemblies, pivot blocks, clamp blocks, and rods that are implanted along a patient""s spine to fix two or more adjacent vertebrae relative to one another. The system generally includes a swing bolt anchor screw, a pivot block receivable on the swing bolt, and a clamp block receiving a rod therethrough that is pivotally attachable to the pivot block. In addition, the system includes one. or more fixed anchor screws, and clamp assemblies for receiving the rod therein. The clamp assemblies and pivot block are receivable on the anchor screws by spindles that thread along a threaded portion of the anchor screws.
During use, vertebrae to be treated are surgically exposed, and an arrangement of anchor screws and clamp accessories are selected. For example, a fixed anchor screw may be screwed into each of the vertebrae on either side of a first vertebra. A rod is selected that may extend between the fixed anchor screws and that may be bent to conform to the shape of the anatomy encountered. The rod is inserted through a loose clamp block, and the rod is placed in clamp assemblies that are received over the fixed anchor screws.
A swing bolt anchor screw is then screwed into the first vertebra adjacent the rod, and a pivot block is received on the swing bolt screw. The clamp block and/or pivot block are adjusted such that the clamp block may be engaged with a pivot on the pivot block. A set screw may then be screwed into the clamp block to secure the clamp block to the pivot. A pair of set screws are also screwed into the clamp block to secure the rod within the clamp block. Preferably, a pair of such systems are implanted on either side of the vertebrae.
During the procedure, it may be desirable to adjust the vertebrae relative to one another. Once the system(s) is(are) connected as described above, the set screws may be loosened and the rod(s), clamp block(s), and/or pivot block(s) may be adjusted, e.g., by moving the spindle(s) to adjust the height of the pivot block(s) and/or clamp assemblies on the anchor screws, by pivoting the swing bolt anchor screw(s), and/or pivoting the clamp block(s) relative to the pivot block(s). Once the vertebrae have been moved into a desired position, the set screws may be tightened, and the spindles secured in position by crimping the walls surrounding the spindles.
An advantage of this system is that the swing bolt anchor screw, pivot block, and clamp block arrangement allows adjustment of the system about two axes, i.e., the axis of the swing bolt anchor screw and the axis of the pivot on the pivot block. However, because the system of the ""166 patent is polyaxial, i.e., may pivot about multiple axes, there is greater risk of the system coming out of alignment when the patient resumes normal physical activity.
This system is also very complicated, involving six parts, including three set screws, that are mounted on each swing bolt anchor screw. In addition, because the swing bolt is threaded, an intricate spindle device is required in order to allow the pivot block and clamp assemblies to be threaded onto the swing bolt, and still control their orientation about the axis of the swing bolt. Thus, because of its complexity and many intricate parts, this system may be expensive to manufacture and/or difficult to implant.
Accordingly, apparatus and methods for stabilizing, adjusting, and/or fixing vertebrae would be considered useful.
The present invention is directed to anchor screw assemblies, spinal fixation systems including such anchor screw assembles, and methods for stabilizing, adjusting, or otherwise fixing adjacent vertebrae using such spinal fixation systems.
In accordance with one aspect of the present invention, an anchor screw assembly is provided that includes a screw having a first threaded portion, and a second head portion. A swing bolt is pivotally coupled to the second portion of the screw. The swing bolt defines a first axis, and includes a noncircular region extending along the first axis, the noncircular region having a noncircular cross-section and a substantially smooth wall. In addition, the swing bolt may include a threaded region on its end opposite the screw.
A clamp assembly is provided that includes first and second clamp portions that are receivable on the swing bolt. Each clamp portion has a noncircular first passage therethrough for receiving the noncircular region of the swing bolt therethrough. Thus, the noncircular region and the first passage have like cross-sections, thereby preventing rotation of the clamp assembly with respect to the swing bolt about the first axis when the noncircular region of the swing bolt is received in the first passages.
In addition, the first and second clamp portions have cooperating grooves therein, the cooperating grooves together defining a second passage extending along a second axis substantially transversely to the first axis when the first and second clamp portions are received on the swing bolt. The clamp assembly also defines a third axis extending along a centerline of the clamp assembly, e.g., from the first passage towards the second passage. The second axis, and consequently the second passage, may extend substantially perpendicular to the third axis, or may define an acute angle with the third axis.
A fastener is also provided for securing the clamp assembly on the swing bolt. Preferably, the fastener is a nut, such as a twelve (12) point nut or a hex nut, that may be threaded onto the threaded region of the swing bolt to secure the clamp assembly on the swing bolt.
In a preferred embodiment, the second portion of the screw includes a shoulder, and the clamp assembly may substantially engage the shoulder when the clamp assembly is fully secured on the swing bolt, thereby preventing the swing bolt from pivoting with respect to the screw. More preferably, the shoulder is radiused about a pivot point on the second portion, and the lower clamp portion includes a recess adjacent its lower surface that intersects the first passage. The recess has a matching radiused shape for slidably receiving the shoulder therein as the clamp assembly pivots about the pivot point, i.e., before the clamp assembly is fully secured on the swing bolt.
In accordance with another aspect of the present invention, a spinal fixation system is provided that includes a first anchor screw assembly, such as that described above. The first anchor screw assembly includes a first screw having a threaded portion, and a swing bolt pivotally coupled to the screw and including a noncircular region. The spinal fixation system also includes a plurality of clamp assemblies, including a first passage for receiving the first swing bolt therethrough, and a second passage for receiving an elongate member, e.g., a substantially rigid rod, therethrough. The dimensions of each clamp assembly may be different, e.g., including a second passage that is at one of a plurality of distances from the first passage and/or that is oriented at a predetermined angle along the clamp assembly.
For example, a first clamp assembly may include a first passage for receiving the first swing bolt therethrough. The first passage has a similar cross-section to the noncircular region of the swing bolt. The first clamp assembly includes a second passage therethrough along a second axis substantially transverse to the first axis. A fastener may be used for securing the first clamp assembly on the swing bolt. Thus, when the first clamp assembly is received on the first swing bolt, the first clamp assembly is fixed in a predetermined orientation with respect to a first pivot axis of the first swing bolt.
The spinal fixation system also includes a second anchor screw assembly including a second screw having a threaded portion and a hub, and a second clamp assembly receivable on the hub. The second screw may be a fixed screw or, preferably, a swing bolt anchor screw, similar to that described above. The second clamp assembly includes a third passage therethrough along a third axis. The second screw assembly may be oriented, when implanted, such that the third axis is substantially transverse to the first axis. Optionally, additional anchor screw assemblies may also be provided.
Finally, the spinal fixation system also include an elongate member, such as a substantially rigid rod, that is receivable through the second and third passages.
In accordance with another aspect of the present invention, a method is provided for simple alignment or otherwise stabilizing vertebrae relative to one another using a plurality of swing bolt anchor screw assemblies, such as those described above. A threaded portion of a first swing bolt anchor screw is screwed into a first vertebra until a first pivot axis of the first swing bolt anchor screw is generally parallel to the spinal axis. A threaded portion of a second swing bolt anchor screw is screwed into a second vertebra adjacent the first vertebra until a second pivot axis of the second swing bolt anchor screw is substantially transverse to the first pivot axis. If desired, a third anchor screw (or more) may be screwed into other vertebra adjacent to the first vertebra.
An angle of one or more swing bolts on the first and second swing bolt anchor screws may be adjusted about the first and second pivot axes. Lower clamp portions may be placed on the swing bolts of the first and second swing bolt anchor screws, either before or after the angle adjustments described above. A rod may be placed on the lower clamp portions, e.g., when the grooves in the lower clamp portions have been properly aligned with one another. Thus, the rod may extend between the first and second anchor screws, and between any additional anchor screws added generally in a straight line. In addition, if desired, the rod may be bent, e.g., in a single plane, to a predetermined configuration based upon anatomy encountered before securing the rod on the swing bolts. Preferably, the rod is bent and secured to the clamp assemblies such that it is curved in the sagetal plane (the plane that may be seen from a lateral view of the patient) and substantially straight in the coronal plane (the plane that may be seen from an anterior or posterior view of the patient).
Upper clamp portions may be secured on the swing bolts of the first and second swing bolt anchor screws, thereby securing the rod between the upper and lower clamp portions. For example, a nut or other fastener may be threaded onto the swing bolt after the upper and lower clamp portions, thereby securing the rod between the upper and lower clamp portions and/or securing the clamp assemblies on the swing bolts. These fasteners may also be loosened to allow adjustment of the vertebrae relative to one another, and then the fasteners may again be tightened to fix the vertebrae in desired relative positions.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.